JPS60235514A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To keep the ratio of currents at a reference side and an output side to a prescribed value with high accuracy without being affected by the condition such as a current amplification factor of each transistor (TR) by constituting the titled circuit with a current share circuit comprising a multi-collector TR. CONSTITUTION:An emitter of the multi-collector TrQ3 and a collector of a TrQ4 are connected together so as to constitute the current circuit of the reference side and collectors of Trs Q5, Q6 are connected together so as to constitute a current circuit of the output side. Then the area of the two collectors of the TrQ3 is made equal, a diode D2 is constituted of an NPN Tr whose collector and base are connected, for example, and the emitter area of the TrQ6 is, e.g., doubled to the emitter area of the Tr constituting the diode D2. Thus, when the current amplification factor of each Tr is sufficiently larger than ''1'' a reference current from an N1 and an output current I2 from an N2 are made equal.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a current mirror circuit, and more particularly to a current mirror circuit with improved accuracy at low current ratios.

(Technical Background) A current mirror circuit is a circuit that can set the ratio of the reference side current to the output side current to a predetermined value, such as "1". Widely used for utensils, etc. In such a current mirror circuit,
It is required that the ratio between the current on the reference side and the current on the output side be maintained at a predetermined ratio with high accuracy even when various conditions such as power supply voltage and ambient temperature change.

(Conventional technology and problems) FIG. 3 shows an example of a conventional current mirror circuit.

The circuit shown in the figure includes a diode D1 connected between the collector of the PNP transistor Q1% and the ground, and an NPN transistor Q2 whose base is connected to the collector of the transistor Q1 and whose emitter is grounded.

In the circuit of FIG. 3, v! of transistor Qt! lB
The current 11 flowing to the emitter of the transistor Q1, that is, the current on the reference side, is determined according to the magnitude of . The collector current 1!1 of the transistor Ql is almost the emitter current It
The diode D1 is caused by the current ■l' equal to
A predetermined forward voltage is generated across the terminal. Since this forward voltage becomes the base-emitter voltage of transistor Q2, collector current 1. is approximately equal to the current 11' and therefore to the current II. In this way, a current I2 on the output side is obtained which is approximately equal to the current Il on the reference side.

The ratio of current work 1 and work 2 is determined by the following formula. P.N.
P-type transistor Q! When the current amplification factors of the NPNPNP transistors are βli- and β2, respectively, the following equations hold true.

These equations (1) and (2) are satisfied. Incidentally, in monolithic ICs and the like, the current amplification factor of a PNP transistor is generally small. Therefore, according to equation (3), the ratio of the current 11 and the current 2 mainly depends on the current amplification factor βl of the PNP transistor Q1. For example, if β1=50 and β=100, then the current 1. It can be seen that the ratio of I2 and I2 is not completely @1# and has an error of about 4%. That is, the conventional current mirror circuit has a problem in that the accuracy of the ratio between the reference side current and the output side current is not very good.

(Object of the invention) The object of the present invention is to solve the problems of the conventional type described above.
In a current mirror circuit, based on a structure that uses a current distribution circuit etc. composed of multi-collector transistors, the current on the reference side and the current on the output side are independent of various conditions such as the current amplification factor of each transistor. The objective is to maintain the ratio between the

(Structure of the Invention) According to the present invention, a current distribution circuit, a pace and an emitter which distributes a first current flowing in accordance with the magnitude of a bias current or voltage into a second and a third current is provided. first and second transistors each connected in common and applying the second current to the common pace circuit; and a third transistor having a diode connected between the pace emitters and receiving the third current to the pace. , operate so that a current obtained by combining the first current and the collector current of the first transistor becomes equal to a current obtained by combining the collector current of the second transistor and the collector current of the third transistor. This is achieved by providing a current mirror circuit featuring:

(Example of the invention) Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows the configuration of a current mirror circuit according to one embodiment of the present invention. The current mirror circuit in the same figure is a PNP
type multi-collector transistor Q3, an NPNPNP transistor whose pace and emitter are connected together and a common pace circuit connected to one collector of multi-collector transistor Q8 and whose emitters are both grounded; and Q5, a paste to the other collector of multi-collector transistor Q3. is connected and the emitter is grounded.
It is composed of a transistor, a diode D2 connected between the pace emitter of the transistor Q6, and the like. The emitter of multi-collector transistor Q3 and the collector of transistor Q4 are connected together to form a reference side current circuit, and the collectors of transistors Qs and Q6 are connected together to form an output side current circuit. The area of the two collectors of the multi-collector transistor Q3 is made the same, so that the current flowing through these two collectors is equal. In addition, the diode D is actually connected to, for example, an NPNW transistor connected between the collector and the conductor.
Thus, the emitter area of the transistor Q6 is, for example, twice as large as the emitter area of the transistor constituting the diode D2.

In the circuit shown in FIG. 1, the reference current flowing from the node N1 to the ground side is 11, and the output current flowing from the node N2 to the ground side is I2. Also, transistor Q
The emitter current of 3 is 11', the collector current of transistor Q4 is I1'', and the collector current of transistor Q6 is 1.
．． /. In this case 11=r! '+ri'...(
4) Since the transistors Q4 and Qs are connected to each other at their base and emitters, the collector current of the transistor Q6 is the same as the collector current of the transistor Q4. Therefore, these transistors Q4 and The total amount of current flowing at the pace of Qs is 2It
//x becomes. On the other hand, the current flowing through each collector of transistor Q3 is 6 (If'/2) x β1/(1+
βl). The current flowing through the transistor Q6 is as follows. Therefore, 1 2 ; I 2'+ I 1" ...(6). From these equations (4), (5), and (6), therefore, β2+3 In equation (9), β1>l, I2 >1, the second term can be ignored.In other words, it can be seen that if the current amplification factors β1 and I2 of each transistor are sufficiently larger than 1, the current 11 and the current 2 are equal.

As an example, β1=59. When βz=100 and the current ratio is calculated from equation (9), the error between the reference side current 11 and the output side current 2 is approximately 0.2%, which is significantly greater than in the case of the conventional type described above. It can be seen that this has been improved.

FIG. 2 shows a current mirror circuit according to another embodiment of the invention. In the circuit shown in FIG. 1, two PNP transistors Q7 and Qs whose base and emitter are connected to each other are used in place of the multi-collector transistor Q3 in the circuit shown in FIG. The other parts are the same as the circuit of FIG. 1, and the same circuit elements are designated with the same reference numerals.

In the circuit of FIG. 2, the emitter current Il' of transistor Q3 in the circuit of FIG. This has the same magnitude as the current flowing through each collector of the multi-collector transistor Q3 shown in FIG. Therefore, as is clear from the above description, the ratio between the reference side current Il and the output side current I2 has the same value as in the case of FIG.

Note that in the circuits of FIGS. 1 and 2, when the emitter area of transistor Q6 is approximately twice that of other transistors, the error in the current ratio between the reference side and the output side becomes extremely small; Even when the emitter area is not necessarily twice that of the transistor D2, the circuit according to the present invention makes it possible to sufficiently reduce the error in current ratio compared to the conventional circuit.

(Effects of the Invention) As described above, according to the present invention, since a current mirror circuit is configured using a current distribution circuit using a multi-collector transistor, etc., the current ratio error between the reference side current and the output side current is can be made extremely small without being affected by the current amplification factor of each transistor, and it is possible to dramatically improve the performance and reliability of a circuit device using a current mirror circuit.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing a current mirror circuit according to one embodiment of the present invention, FIG. 2 is an electric circuit diagram showing a current mirror circuit according to another embodiment of the present invention, and FIG. 3 is a conventional type FIG. 2 is an electrical circuit diagram showing a current mirror circuit of FIG. Ql, Q7, Ql...PNP type transistor, Q2
1Q4 * Q5 + Q6 ``'NPN type transistor, Qa''/PNP type multi-collector transistor, D
l, D2...diode, vBll...bias power supply. Patent applicant Fujitsu Ltd. Patent application agent Akira Miyagi Patent attorney Nishi,! Kazuyuki Tate Patent Attorney 1) Yukio Patent Attorney Akira Yamaguchi 1st package N, N2 @2shi1 30th 1st

Claims (1)

[Claims] a current distribution circuit that divides a first current flowing into second and third currents according to the magnitude of the bias current or voltage;
first and second transistors, each having a pace and an emitter connected in common and applying the second current to the common pace circuit; and a third transistor having a diode connected between the pace emitters and receiving the third current in the pace. a current that is a combination of the first current and the collector current of the first transistor;
A current mirror circuit characterized in that it operates so that a current obtained by combining the cv collector current and the collector current of the third transistor becomes equal.